The research proposed is focused on physiological interactions between mammals and microorganisms indigenous to their gastro-intestinal tracts. Germfree, gnotobiotic and specific pathogen-free mice and rats are used; microbes that associate intimately with mucosal epithelia receive special emphasis. Our long-term goals are to learn how these microbes remain and proliferate in their habitats and how they influence certain physiological responses in their mammalian hosts. In seeking the first goal, we examine the mechanisms by which the microbes attach and grow on the epithelia. Microbial culture techniques including methods for culturing oxygen-intolerant anaerobic bacteria, frozen-section histology, immunofluorescence techniques and transmission and scanning electron microscopy are used to characterize the associations. Large quantities of microbial cells are produced. Components of those cells are isolated, purified and assayed in studies of the mechanisms by which the microbes attach to epithelia. In seeking the second goal, we examine the mechanisms by which certain of the microbes depress the activity levels of alkaline phosphatase and other enzymes in the intestinal epithelium of mice. Microbial culture and biochemical techniques including spectrophotometry, column chromatography and polyacrylamide gel electrophoresis are used in characterizing the enzymes in the intestinal epithelia. Germfree mice are monoassociated with indigenous microbes that attach to epithelial surfaces. These gnotobiotes are used in experiments designed to determine whether or not the microbes depress the activity levels of the enzymes in microvillous membranes by altering the migration rate of intestinal epithelial cells.